The invention relates to a catalyst which can be employed for the hydrogenation of functional groups of organic compounds in the presence of water, in particular for the hydrogenation of nitro groups in nitroaromatics to give the corresponding amines in the presence of water or for the hydrogenation of aldoses and ketoses to the corresponding sugar alcohols in the presence of water, and to a process for its preparation.
The industrially most frequent applications of the hydrogenation of functional groups of organic compounds are the hydrogenation of aldoses or ketoses to the corresponding sugar alcohols or of nitroaromatics to the corresponding amines.
The hydrogenations are in general carried out either in a fixed-bed reactor or in a batch reactor. On the industrial scale, hydrogenations are most frequently performed in the liquid phase using a suspended catalyst, the processes differing by the reaction temperature, the pressure, the catalyst, the solvents and the nature of the reaction procedure. Catalysts used here are various catalyst systems, such as, for example, nickel-containing catalysts. The catalytic hydrogenation of glucose to sorbitol using a nickel-SiO2xe2x80x94Al2O3 catalyst is disclosed in NL 8 102 190. The use of nickel-copper supported catalysts for the hydrogenation of glucose is disclosed in DD 217 996. Supports used are SiO2, Al2O3 and SiO2xc2x7Al2O3. In DD 156 175, the obtainment of sorbitol by hydrogenation of glucose in the presence of an Nixe2x80x94SiO2 catalyst is described. According to patent specification SU 565 040, hydrogenation to sorbitol on Raney nickel catalysts at a catalyst concentration of 5 to 6%, temperatures of 110 to 150xc2x0 C. and pressures of 40 to 60 bar proceeds with obtainment of good yields after 1 to 2 hours. U.S. Pat. No. 4,694,113 describes a two-stage process for the hydrogenation of glucose to sorbitol, approximately 95% of the glucose being hydrogenated in the presence of a nickel catalyst to give sorbitol in the first stage and, after removal of the nickel catalyst, the remainder of the glucose being hydrogenated to sorbitol using an Ru catalyst.
JP 551 33 33 discloses the hydrogenation of 2,4-dinitrotoluene and 2,6-dinitrotoluene in the presence of the catalysts Pd/C, Raney nickel, Raney cobalt or platinum black.
EP-A 98 681 discloses a nickel-kieselguhr supported catalyst for the hydrogenation of dinitrobenzophenone to the corresponding diamine.
In DE-A 35 37 247, the hydrogenation of dinitro compounds to the diamines in the presence of modified Raney nickel catalysts is described.
EP-A 0 335 222 discloses the use of nickel-Al2O3/ZrO2 supported catalysts for the hydrogenation of nitrites, aromatics, nitro compounds and olefins. The specification discloses, inter alia, the simultaneous precipitation of nickel, zirconium and aluminum on supports at 50 to 120xc2x0 C. and at a pH of 7.3 to 9.0, the supports employed being active carbon, Al2O3, SiO2, kieselguhr and others.
SU patent 28 31 85 discloses nickel-Al2O3/ZrO2 catalysts which were prepared by precipitating nickel and Al2O3 on ZrO2.
According to the teaching of U.S. Pat. No. 2,564,331, a nickel-ZrO2 catalyst is prepared by precipitating a nickel and zirconyl carbonate mixture with subsequent washing, drying and reduction at 250 to 350xc2x0 C., the catalyst containing at most 10 mass % of ZrO2.
The precipitation of insoluble carbonates is also disclosed in DE-B 1 257 753, the precipitation process being induced by evaporation of CO2 and NH3 from a mixed salt solution of ammonium zirconyl carbonate and nickel ammine carbonate.
EP-A 0 672 452 discloses catalysts for the hydrogenation of organic compounds, which essentially contain 65 to 80 mass % of nickel, calculated as NiO, 10 to 25 mass % of SiO2, 2 to 10 mass % of zirconium, calculated as ZrO2 and 0 to 10 mass % of aluminum, calculated as Al2O3, the sum of the content of SiO2 and Al2O3 being at least 15 mass %. These catalysts are prepared by addition of an acidic aqueous solution of Ni, Zr and, if desired, aluminum compounds to a basic aqueous solution or suspension of silicon compounds and, if desired, aluminum compounds. During the precipitation, the pH is first lowered to 4.0 to 6.5 and subsequently adjusted to 7 to 8. The precipitation product is dried, calcined and shaped.
The previously known nickel hydrogenation catalysts all have the disadvantage that under the hydrothermal reaction conditions both of the hydrogenation of glucose and of nitroaromatics a rapid aging of the catalysts occurs.
The technical problem underlying the present invention is thus to make available nickel-containing supported catalysts which, in particular under the hydrothermal reaction conditions of the hydrogenation of glucose and nitroaromatics, have a higher lifespan than the conventional catalysts.
This problem is achieved according to the invention by making available a catalyst, in particular for the hydrogenation of functional groups of organic compounds, in particular for the hydrogenation of glucose to sorbitol or of nitro groups in nitroaromatics to the corresponding amines in the presence of water, comprising nickel on a support, the catalyst being reduced and stabilized, contains nickel crystallites having a monomodal nickel crystallite size distribution, a nickel content of 25 to 60 mass % (based on the total mass of the catalyst), in particular 25 to 59 mass % (based on the total mass of the catalyst) and a degree of reduction of at least 65%. The degree of reduction is determined after a one-hour afterreduction of the stabilized catalyst at 100xc2x0 C. in a stream of hydrogen (loading: 1 000 v/vh).
The invention solves this problem also by the making available of a process for the preparation of such a catalyst.
The invention provides in a particularly preferred embodiment that the above-mentioned catalyst has a monomodal nickel crystallite size distribution, the maximum of the nickel crystallite size distribution being 25 to 90 angstroms, in particular 30 to 90 angstroms.
In a further preferred embodiment, it is provided that the above-mentioned catalyst is supported on a zirconium-containing support, preferably contains ZrO2, ZrO2HfO2, SiO2xc2x7ZrO2, SiO2xc2x7ZrO2HfO2 or mixtures of at least two substances thereof or consists of these.
In a particularly preferred embodiment, the SiO2 content is 0 to 40 mass % (based on the total mass of the catalyst). In a further preferred embodiment, the ZrO2 content is 20 to 75 mass % (based on the total mass of the catalyst). In a further preferred embodiment, the HfO2 content is 0 to 7.5 mass % (based on the total mass of the catalyst).
In a particularly preferred embodiment of the invention, the reduced and stabilized catalysts can be employed as powders having particle sizes of 1 to 100 xcexcm, preferably of 2 to 30 xcexcm. Of course, shaped articles can also be employed.
The catalysts according to the invention are distinguished in an advantageous and surprising manner by their prolonged lifespan with identical or improved catalytic activity compared with conventional catalysts. Catalysts of the monomodal nickel crystallite size distribution according to the invention have, in particular under hydrothermal reaction conditions, a considerably prolonged lifespan compared with conventional catalysts.
In connection with the present invention, a monomodal nickel crystallite size distribution is understood as meaning a distribution of the nickel crystallites according to which only a maximum of the crystallite size distribution is present.
In connection with the present invention, the term degree of reduction is understood as meaning the proportion of the metallic nickel in the total nickel content of the stabilized catalyst which is present after a one-hour afterreduction at 100xc2x0 C.
The invention also relates in a further embodiment to a process for the preparation of the above-mentioned catalyst. The invention thus also relates to a process for the preparation of a nickel-containing supported catalyst, in particular of a catalyst for the hydrogenation of carbonyl groups in aldoses or ketoses in the presence of water and of nitro groups in nitroaromatics to the corresponding amines in the presence of water, where, by precipitation from an Ni2+- and Zr4+-containing solution with a basic solution, in particular a solution of NaOH, NaHCO3 or Na2CO3 or a mixture of at least two of these substances, up to a pH of 8 to 9 a precipitation product is obtained which is calcined at temperatures from 300xc2x0 C. to 650xc2x0 C., optionally then inertized, and subsequently reduced with hydrogen at temperatures from 250xc2x0 C. to 550xc2x0 C., in particular 300xc2x0 C. to 550xc2x0 C., optionally inertized, and subsequently stabilized.
In a particularly preferred embodiment, the Ni2+- and Zr4+-containing solution additionally contains HF4+. In a further preferred embodiment, the Ni2+ and Zr2+-containing solution or the Ni2+ and Zr4+/Hf4+-containing solution contains silica SiO2, preferably in suspended form. In a preferred embodiment it can be provided that the Ni2+- and Zr4+-containing solution contains nitrates, in particular in the form of zirconyl nitrate.
The precipitation product is thus prepared by addition of the basic solution mentioned to the Ni2+- and Zr4+-containing solution, this addition being carried out until the mixture of the two solutions reaches a final pH of 8 to 9.
The invention provides in a preferred embodiment that the precipitation takes place at temperatures from 60xc2x0 C. to 95xc2x0 C. In the preferred embodiment, it can be provided that, after the precipitation has been carried out, i.e. the final pH has been reached, the suspension obtained is subsequently stirred, for example, for one to two hours before further processing.
In a further embodiment, the invention relates to an aforementioned process, the precipitation product being filtered after the precipitation, washed, preferably with water, and subsequently dried at temperatures from 110xc2x0 C. to 150xc2x0 C. in a nonreducing atmosphere and a precursor catalyst being obtained.
In connection with the present invention, a precursor catalyst is understood as meaning a product which is obtained after the precipitation of the starting components, i.e. of the Ni2+- and Zr4+-containing, optionally Hf4+-containing solution, and optionally of the SiO2 with the basic solution added, filtration, washing with water and drying at temperatures in a nonreducing atmosphere.
According to the invention, in the preparation of the precursor catalyst phases of nickel hydroxynitrate (Ni3(OH)4(NO3)2) or nickel hydroxynitrate (Ni3(OH)4(NO3)3-containing phases, in particular mixtures of nickel hydroxynitrate (Ni3(OH)4(NO3)2), nickel hydroxycarbonate (Ni2(OH)2CO3 4H2O) and nickel hydroxysilicate (Ni3Si2O3(OH)4) or mixtures of nickel hydroxynitrate (Ni3(OH)4(NO3)2) and nickel hydroxide (Ni(OH)2) result having lattice widenings or a sepiolite-like structure (Ni4Zr6O15(OH)2), where OHxe2x88x92 ions can be partially replaced by carbonate ions.
In connection with the present invention, lattice widening is understood as meaning a shift in the interference position to smaller angles.
Either before or after the calcination, the catalyst precursor can be shaped to give tablets, extrudates, cushion-like articles, spheres or the like.
The reduction of the calcined product can be carried out according to the invention both on the powder and on the shaped articles. According to the invention, it is particularly preferred to employ gas loadings in the range from 500 to 3 000 v/v h during the reduction.
According to the invention, it is provided in a preferred embodiment that the catalysts are stabilized after the reduction, preferably using an O2xe2x80x94N2xe2x80x94CO2 mixture.
The invention therefore also relates to the making available of a process for the passivation of a preferably reduced and/or preferably inertized catalyst according to the invention, the catalyst being treated in a process step a) in a CO2xe2x80x94N2 gas mixture having a CO2 content of 0.5 to 10% by vol. at temperatures from 91xc2x0 C. to 350xc2x0 C. for at least 30 minutes, in a process step b) subsequently being cooled in the gas mixture mentioned in step a) to a temperature of at most 90xc2x0 C., then in a process step c) after reaching the temperature of at most 90xc2x0 C. being added in a first passivation phase to the gas mixture oxygen, preferably air, up to a content of 0.2 to 1.5% by vol. of oxygen and the catalyst being treated in the mixture for at least 30 minutes with shaking and then in a process step d) the CO2 content in the gas mixture according to step c) being reduced in a second passivation phase to  less than 0.1% by vol. and the O2 content being increased to 1.5 to 21% by vol.
The procedure according to the invention for the stabilization of the catalyst has the advantage of short stabilization times, at the same time readily reactivatable catalysts having very good thermal stability being obtained. In an advantageous manner, the catalysts are particularly uniformly passivated. Indeed, it was surprising that by the treatment with CO2-low inert gases under the conditions indicated, very uniform and readily reactivatable catalysts were obtained.
The invention relates in a preferred embodiment to an aforementioned process, at least the passivation being carried out continuously or in a batch process in a catalyst bed, in particular using a catalyst bed whose height to diameter ratio is in the range from 0.05 to 1.
In a further preferred embodiment, the invention provides an aforementioned process, the concentration of the CO2 during the treatment with the CO2xe2x80x94N2 mixture according to process step a) being 1 to 2.5% by vol.
In a further preferred embodiment, the invention provides an aforementioned process, the gas loading during the treatment with the CO2xe2x80x94N2 mixture according to process step a) being 500 to 10 000 v/v h. In a further preferred embodiment, the invention proposes that the aforementioned process, a gas loading during the treatment with the CO2xe2x80x94N2 mixture according to process step a) and/or during the treatment with the CO2xe2x80x94N2xe2x80x94O2 gas mixture according to process steps c) and d) is 100 to 3 000 v/v h.
The invention provides in a further preferred embodiment that the aforementioned process, the treatment in the CO2xe2x80x94N2xe2x80x94O2 gas mixture according to process steps c) and d), is carried out for a period of time of 30 minutes to 8 hours.
The invention relates in a further embodiment to an aforementioned process, the time period of the treatment according to process step c), i.e. of the first passivation phase, to the time period of the process step according to process step d), i.e. the second passivation phase, being 9:1.
In a further preferred embodiment, the invention relates to an aforementioned process, the temperature of the treatment of the catalyst with the CO2xe2x80x94N2xe2x80x94O2 gas mixture according to step c) and/or step d) being 50 to 70xc2x0 C.
In a further preferred embodiment, the invention provides an aforementioned process, the CO2 concentration in the CO2xe2x80x94N2xe2x80x94O2 gas mixture during the treatment according to process step c) being 0.5 to 1.5% by vol. In a preferred manner, the invention can provide for the CO2 content of the mixture from step a) for carrying out step c) to be reduced, for example to the aforementioned range.
According to a further preferred embodiment of the present invention, an aforementioned process is made available, the 02 concentration in the CO2xe2x80x94N2xe2x80x94O2 gas mixture during the treatment according to process step c) being 0.25 to 0.8% by vol.
In a further preferred embodiment of the invention, the O2 concentration during the treatment according to process step d) is 5 to 10% by vol.
The invention relates in a further embodiment to an aforementioned process, it being provided that the shaking of the catalyst bed according to process step c) and/or d) is performed at time intervals of 10 to 20 minutes over a period of time of 0.5 to 2 minutes in each case. It is advantageous to set shaking rates of 10 to 50 Hz.
Of course, it is also possible, in particular in the case of pulverulent catalysts and catalysts having very high solidifies, to set the catalyst bed in motion by producing a fluidized layer or by arrangement in a rotary furnace. An important standpoint of the present invention is to agitate the catalyst at least occasionally in the oxygen-carbon dioxide-nitrogen mixture during the passivation phases according to process steps c) and d), for example in an agitated bed.
The stabilization can also be carried out in a particularly preferred manner by stabilizing in a stream of nitrogen having an oxygen content of 0.1 to 1% by vol. and a CO2 content of 0.6% by vol. at temperatures below 80xc2x0 C.
Of course, it is also possible to carry out the stabilization of the reduced catalyst obtained according to the invention in another manner, for example according to the teaching of U.S. Pat. No. 4,090,980, which is additionally included in the disclosure content of the present application with respect to the process parameters for the stabilization of catalysts.